1. Technical Field
The present invention relates to a polarization conversion device, and a polarization conversion unit and a projection type video apparatus that are provided with the polarization conversion device.
2. Related Art
A projection type video apparatus such as a liquid crystal projector modulates light emitted from a light source device according to image information, and enlarges this modulated optical image and projects it onto a screen. In this liquid crystal projector, a polarization conversion device is used to improve efficiency for light utilization. The polarization conversion device divides light (hereinafter, referred to as random light) including randomly polarized light (P-polarized light and S-polarized light whose polarization planes are orthogonal to each other, or light in which linearly polarized light having various polarization-plane directions is mixed), which is emitted from a light source device, into a plurality of intermediate light beams, and converts these divided intermediate light beams into one kind of linearly polarized light for collective emission.
This polarization conversion device has a configuration in which a polarization separation film and a reflective film are disposed alternately in a transparent member to form a polarization beam splitter array, and a phase difference plate is provided on a surface of the polarization beam splitter array. A plurality of phase difference plates is disposed at a position corresponding to the polarization separation film at the side of a light emitting plane of a transparent member for each predetermined interval (refer to JP-A-2000-298212).
As the phase difference plate in the related art, ½ wavelength plate formed of an organic material, for example, a polycarbonate film is used, and this ½ wavelength plate and the polarization beam splitter array are bonded to each other by an organic adhesive.
As a method of manufacturing the polarization conversion device, a transmissive substrate such as colorless transparent glass, which includes a polarization separation film and a reflective film formed on both principal planes, respectively, is repeatedly laminated to form a laminated body, and a ½ wavelength plate is adhered with an adhesive to an emission plane of a lens array, which is obtained through a cutting at an angle of 45 deg with respect to an incidence plane.
The polarization conversion device manufactured in this way is mounted in an optical engine of liquid crystal projector in a state of being assembled in a frame having a planar rectangular shape (refer to Japanese Patent No. 3610764).
Progress has been made regarding the high output and the short arc length of a white-colored light source lamp, and a thermal load with respect to the polarization beam splitter array and the ½ wavelength plate bonded to the polarization beam splitter array has been increased, such that the use of quartz crystal as a material making up the ½ wavelength plate is considered. Here, a liquid crystal projector in which as the adhesive, an adhesive of an ultraviolet curable resin or an inorganic material that is excellent in heat resistance and light resistance is used, in a case where the ½ wavelength plate is disposed to be bonded to an emission-side side surface of the polarization beam splitter array, and accordingly, compulsory air cooling using a cooling fan is unnecessary is disclosed (refer to JP-A-2009-103863).
In addition, in regard to a combination of the ½ wavelength plate formed of quartz crystal and the polarization beam splitter array, from problems related to a mutual flatness and positioning, or the like, there is disclosed a polarization conversion unit that includes a polarization separation device (polarization beam splitter) including a plurality of polarization separation films that is disposed to be inclined with respect to incident light beams and that separates the incident light beams into two kinds of linearly polarized light beams, a plurality of reflective films that is disposed alternately and parallel between the respective polarization separation films and that reflects any one side of the linearly polarized light beams that are separated by the polarization separation film, and a transmissive member provided with the polarization separation film and the reflective film; a plurality of phase difference plates that is formed of a quartz crystal member that converts a polarization plane of any one side of the linearly polarized light beams that are separated by the polarization separation film into a polarization plane of the other side of the linearly polarized light beams; and a spacer member that adheres an end of the phase difference plate to a beam emission side of the transmissive member (refer to Japanese Patent No. 4329852). Here, in the spacer member, adhesion correction of the object to be adhered is allowed, and a dimension G of an interval between the polarization separation device array and the phase difference plate is optimally with a range of 0.01 mm≦G≦0.3 mm.
In recent years, along with an increasing request for a long operating life as an optical part, there is a problem related to deterioration of the adhesive.
To solve such a problem, there is disclosed a bonding method in which as means for bonding two sheets of transmissive substrates formed of glass, quartz crystal, or the like, a bonding film, which includes, on a surface thereof, an Si skeleton having a siloxane (Si—O) bond and having a degree of crystallinity of 45% or less and an elimination group consisting of an organic group coupled to the Si skeleton, is formed by a plasma polymerization method, and then an energy is applied to the bonding film, and thereby the elimination group present in the vicinity of the surface of the bonding film is eliminated from the Si skeleton and due to an adhesive property exhibited at a region of the surface of the bonding film, the two sheets of transmissive substrates are bonded (refer to Japanese Patent No. 4337935). Furthermore, in the related art, there is disclosed a polarization conversion device in which a light incidence plane and a light emission plane that is approximately parallel with the light incidence plane are provided, a plurality of transmissive members, polarization separation films, reflective films, phase plates, and plasma polymerized films are disposed along the light incidence plane and the light emission plane, either the polarization separation film or the reflective film is provided on an inclined surface of each of partial transmissive members among the plurality of transmissive members, and the plasma polymerized film is provided on at least one of a surface of an inclined plane of the transmissive member, a surface of the polarization separation film, and a surface of the reflective film (refer to JP-A-2010-60770). In an example of the related art disclosed in JP-A-2010-60770, at least one of between the transmissive member and the reflective film that are adjacent to each other, between the transmissive member and the phase plate that are adjacent to each other, and between the phase plate and the polarization separation film that are adjacent to each other is molecular-bonded by the plasma polymerized film, and the plasma polymerized film includes polyorganosiloxane as a main material thereof.
However, in an example of the related art disclosed in JP-A-2010-60770, there is a problem in that the bonding film formed of a plasma polymerized film is an extremely thin film of several tens of nm, and when an attached substance such as dust and contaminant attaches to a surface of a transmissive substrate while the bonding film is formed on the surface of the transmissive substrate using a plasma polymerization method, the height of the attached substance becomes far larger than the film thickness of the bonding film, such that the transmissive substrates are not bonded at a predetermined region around a region to which the attached substance is attached, and bubbles or the like are introduced into the region and thereby a severe adverse effect may result in regard to an optical characteristic, the bonding reliability, and the product lifetime.
Therefore, as a related art not using the plasma polymerized film, PCT Japanese Patent Domestic Re-publication No. WO98/23993 may be exemplified. In PCT Japanese Patent Domestic Re-publication No. WO98/23993, an optical block is configured in such a manner that optical parts such as a PBS (polarization beam splitter), a mirror, and ½ wavelength plate are mounted with respect to a groove formed in a substrate. The PBS is formed through a deposition of, for example, TiO2 or the like on a surface of a glass plate, and is press-fitted into the substrate at a predetermined angle with respect to an incidence direction of light. The mirror is formed through a deposition of, for example, aluminum or a dielectric multi-layer film on a surface of a rectangular glass plate so as to be able to reflect incident light. The mirror is mounted on the substrate at an angle of reflecting an S-wave that is separated and reflected by the PBS to an emission-side. The ½ wavelength plate is formed by adhering a ½ phase difference film obtained through a uniaxial drawing of, for example, polycarbonate, polyvinyl alcohol, or polyethylene terephthalate to a rectangular glass plate. The ½ wavelength plate is mounted at a position where the S-wave reflected by the mirror is incident, and polarizes the S-wave into a P-wave and outputs the P-wave. As described above, the optical block is configured by the PBS, the mirror, ½ wavelength plate, or the like, such that randomly polarized light including the incident P-wave (P-polarized light) and the S-wave (S-polarized light) may be emitted as the unified P-wave (P-polarized light) only, and an incidence-side area and an emission-side area of the optical block may be substantially the same as each other.
Quartz crystal has not only a birefringent property but also an optical rotatory property, and there is a well-known problem in that this optical rotatory property has an effect on a phase difference characteristic of wavelength plate formed of quartz crystal.
In regard to this problem, there is proposed a ¼ wavelength plate configured in such a manner that two wavelength plates formed of an optical crystalline material having an optical rotatory power are disposed and laminated such that respective crystal optical axes thereof intersect with each other at a predetermined angle, and a relationship of a birefringent phase difference, an optical axis azimuthal angle, an optical rotatory power, and an angle made by a rotary axis and a neutral axis of both wavelength plates satisfy a predetermined relational equation obtained by an approximate equation through an analysis of a polarized light trajectory using a Poincare sphere, and as a result thereof, the reduction in the effect caused by the optical rotatory power and the improvement in a characteristic in a broad band are attempted (refer to JP-A-2005-158121).
In addition, in regard to one sheet of a wavelength plate formed of an inorganic material such as quartz crystal, there is proposed a ¼ wavelength plate showing an excellent optical characteristic, which is formed of a crystalline plate of an inorganic material such as quartz crystal that has a birefringent property and an optical rotatory property and shows a sufficient light resistance and reliability against a bluish purple laser showing a high output with a short wavelength, and in which an ellipticity may be set to an optimal value, that is, a high value of 0.9 or more and substantially near 1 (refer to JP-A-2010-134414).
However, in the example of the related art disclosed in PCT Japanese Patent Domestic Re-publication No. WO98/23993, in regard to the PBS, a dielectric multi-layer film, which is formed by alternately and repeatedly laminating TiO2 (high refractive index material) and SiO2 (low refractive index material), or the like, is deposited on a surface of a glass substrate, and thereby a polarization separation film is formed. Accordingly, there is a concern that separation may occur at the interface between the glass substrate and the polarization separation film due to a thermal distortion caused by a difference in a thermal expansion coefficient, as well as that heat dissipation in the glass plate may be restricted, such that the strong demand for heat resistance and a long operating life is not sufficiently satisfied.
Here, in consideration of a heat dissipation effect, it may be considered to use a quartz crystal plate instead of the glass substrate in the PBS, but quartz crystal has an optical rotatory property as well as a birefringent property, such that in the configuration where the glass plate is simply substituted with the quartz crystal plate, it is difficult to solve a problem related to the optical rotatory property through only the determination of a crystalline optical axis such that a phase difference does not occur from a relationship of the polarization plane of the incident linearly-polarized light, and therefore there is a problem in that an optical action caused by an optical rotatory power of the incident linearly-polarized light occurs.
Here, it may be considered to realize the polarization separation device capable of transmitting the incident P-polarized light without causing any optical action through an application of a technical idea in the example of the related art disclosed in JP-A-2005-158121 and JP-A-2010-134414 in which the effect on the phase difference caused by the optical rotatory power is focused, but it is difficult to solve the problem posed by the present inventors through an application of JP-A-2005-158121 and JP-A-2010-134414 that are related to the optical rotatory power compensating technology, which improves the effect caused by the optical rotatory power with respect to the birefringent phase difference which the ¼ wavelength plate formed of quartz crystal has, to PCT Japanese Patent Domestic Re-publication No. WO 98/23993 without modification.